A deletion upstream of the degron of AcIAA27 leads to auxinic herbicide resistance in Arctotheca calendula.

BACKGROUND

Two populations of Arctotheca calendula (capeweed) from near Naracoorte, South Australia, were not controlled by 2,4-D. These populations were investigated for resistance to 2,4-D and other auxin herbicides. Aux/IAA genes were investigated for potential mutations.

RESULTS

Dose response experiments confirmed both populations were resistant to 2,4-D and also cross-resistant to MCPA, dicamba, triclopyr and picloram. The level of 2,4-D resistance in the populations was unchanged by pretreatment with the P450 inhibitor, malathion. Compared to the susceptible populations, a 12 bp deletion and a point mutation (Val116Asp) were identified upstream of degron region in AcIAA27 of R1, located 29 and 19 amino acids away from the degron. However, R2 did not have this mutation. Overexpression of AcIAA27 and AcIAA27 in Arabidopsis increased survival of plants treated with 2,4-D, dicamba, fluroxypyr and picloram, compared with controls. There was no significant difference in the level of resistance to auxin herbicides between Arabidopsis lines expressing AcIAA27 and AcIAA27.

CONCLUSION

Our study demonstrated that resistance to 2,4-D and other auxin herbicides in capeweed population R1 is due to a deletion in AcIAA27. However, the Val116Asp mutation did not appear to contribute to resistance. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.